CrystalReports 2008 SDK PrintToPrinter Hangs

Question

Hi,
I am using CrystalReports 2008 SDK (CrystalDecisions.CrystalReports.Engine) in a VB.NET 2008 Application.  The application is Multi-Threaded  and each thread can send a report to a printer asynchronously.  The application is currently limited to 8 of these threads.  The application prints any where from 50 to 100 reports a minute.  Once or twice a week, all eight threads will hang on the call to CrystalDecisions.CrystalReports.Engine.ReportDocument.PrintToPrinter(1, False, 1, 1).
Below is a sample of the code from the threads...
Private ManifestReport As New CrystalDecisions.CrystalReports.Engine.ReportDocument
Private Sub PrintReport()
                SubmitReport(EntryID, ReportName, PrinterName, Me.ManifestReport)
End Sub
Private Sub SubmitReport(ByVal EntryId As Long, _
                             ByVal ReportName As String, _
                             ByVal PrinterName As String, _
                             ByRef Report As CrystalDecisions.CrystalReports.Engine.ReportDocument)
        Report.Load(ReportName)
        ' Set the Report/SubReport Data Sources
        For i As Integer = 0 To Report.Database.Tables.Count - 1
            Report.Database.Tables(i).SetDataSource(GetDataSource(Report.Database.Tables(i)))
        Next
        For Each subReport As CrystalDecisions.CrystalReports.Engine.ReportDocument In Report.Subreports
            For Each subreportTable As CrystalDecisions.CrystalReports.Engine.Table In subReport.Database.Tables
                subreportTable.SetDataSource(GetDataSource(subreportTable))
            Next
        Next
        ' Assign the EntryId to be Printed
        Report.SetParameterValue("EntryId", EntryId)
        ' Send Report to Printer
        If Not Me.PrintToFile Then
                Report.PrintOptions.PrinterName = PrinterName
                Report.PrintToPrinter(1, False, 1, 1)
        Else
            Report.ExportToDisk(CrystalDecisions.Shared.ExportFormatType.CrystalReport, "C:\Temp" & ReportName.Substring(ReportName.LastIndexOf("\")) & "_" & (EntryId Mod 56) & ".rpt")
        End If
End Sub

Answer 1

Elaine,
Thank you for your response! 
I do already have code in my thread to cleanup the Report. I created a Dispose routine that is called by the application that creates and destroys the thread.
    If ManifestReport IsNot Nothing Then
        If ManifestReport.IsLoaded Then ManifestReport.Close()
        ManifestReport.Dispose()
        ManifestReport = Nothing
    End If
In order to speed up the processing of the application, I create the Database Adapters and Datasets when the application starts up and then I just re-fill them each loop of the main application.  This helped to eliminate memory leaks and drastically increased performance.  When monitoring the application the memory usage and the number of threads fluctuate but do not grow.
The application is printing approximately 50 Manifest Reports when there is information in the database to print.  The application reads all the data necissary to print all of the reports.  Then the application will loops through the reports and creates a thread to print each report.  Only eight threads can be active at any given time.  A request to print the set of Reports occurs approximately every minute.
Thank you,
Bob